Approximately 2.1 million people in the United States are currently living with Limb loss, but the dream of amputees feeling human touch through their prosthetics may be closer to fruition than ever.

A groundbreaking development has led to the creation of a prosthetic limb equipped with fingertip sensors, empowering a standard prosthetic hand to detect and react to Temperature variations as a natural hand would.

This innovation provides amputees with a genuine experience of warmth and coolness in their “phantom” limbs by transmitting thermal data to nerve regions in the remaining part of the limb. These regions are interpreted by the brain as still being connected to the absent hand.

The technology, named the MiniTouch and detailed in a study recently published in Med, is built using readily available, cost-effective components. It also doesn’t necessitate surgical implantation and can be integrated into commercially available prosthetic hands within a few hours.

Being able to detect hot and cold temperatures marks a significant enhancement in prosthetic limb technology, yet it represents more than just a functional upgrade.

The perception of temperature introduces a human dimension to the sense of touch. Experiencing warmth contributes to a deeper sense of embodiment, fostering the feeling that a prosthetic isn’t merely a synthetic aid but an integral part of one’s body.

“We have a colleague who says touch without temperature is like vision without color,” said Solaiman Shokur, the study’s senior author.

Shokur also stated that, right now, researchers are advancing the capabilities of prosthetics to perceive textures as well. At the same time, they are focusing on proprioception, which is the brain’s capacity to be aware of the position and movement of body parts. So, the ultimate goal is to integrate all these elements, creating a complete spectrum of sensations.

Last year, the same team of researchers unveiled findings from a study where they applied thermal electrodes to the residual limbs of amputees. When these electrodes were activated by touching objects with varying temperatures through an attached sensor, participants reported feeling these thermal sensations in their absent hand.

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This phenomenon of experiencing phantom thermal sensations varies among amputees, indicating that the nerves severed during amputation are still present in different areas of the arm’s skin.

Stimulating these specific skin patches with hot or cold items triggers a response along the pathways to the brain that were originally associated with the hand. Consequently, this leads the amputee to perceive those temperatures in their missing limb.

According to Roberto Renda, a participant in a trial related to the study, he was able to “feel the warmth of another person” with his phantom hand for the first time in two decades.

“It’s like having a connection with someone. I would like to feel both of my kids’ hands when I walk down the street with them, holding their hands. That would be nice,” Roberto said.

In the initial study, 17 out of 27 participants experienced these phantom thermal sensations, which played a crucial role in demonstrating the effectiveness of the MiniTouch system.

MiniTouch is a slender, wearable sensor designed to fit seamlessly over a prosthetic finger and connect to specific areas on the skin of the residual limb. These areas are identified for their ability to generate sensations that the amputee feels as though they are coming from the absent hand.

But, even though the 2023 study established that the sensor could assist amputees in sensing temperature, the latest research marks the first instance of its application on a working prosthetic.

Fabrizio Fidati, a 57-year-old amputee, volunteered to test the device with his current prosthesis. He was given three identical bottles filled with water at varying temperatures, including cold (53 degrees Fahrenheit), cool (75 degrees Fahrenheit), and hot (104 degrees Fahrenheit).

His ability to differentiate between the bottles was correct only 33% of the time without the device. However, with the MiniTouch equipped, Fabrizio’s identification accuracy soared to 100%.

Afterward, he was asked to organize identical metal cubes that were either heated or cooled to various temperatures. The use of the temperature-sensitive prosthetics significantly enhanced his ability to do this.

Interestingly, Fidati also noted that the sensations of heat and cold felt through his phantom hand were even more pronounced than those in his intact hand.

Then, the researchers conducted a test where Fidati, who was blindfolded, had to discern whether he was touching another prosthetic hand or study co-author Francesco Iberite’s hand. The warmth from the human hand made it easier for Fidati to make this distinction, though he was not as successful as he might have been with his unaffected arm.

The study’s authors believe that incorporating additional inputs like textures and softness could further refine this ability. So, this test underscores that while temperature perception is crucial, it is merely one component of the complex sensory experience of human touch – suggesting a path toward developing prosthetics that more closely mimic the functionality of a human hand.

Millions of individuals around the globe have undergone limb amputation, prompting scientists and biomedical engineers to tirelessly enhance prosthetics for patients.

Many initiatives aimed at restoring sensation to amputees require internal implants, which, while beneficial, present certain challenges. For instance, surgical interventions are intrusive and carry high costs, both for the procedure itself and for the sophisticated devices they facilitate.

However, the MiniTouch sensor stands apart as it can be effortlessly added to an existing prosthetic within a few hours and utilizes consumer-grade technologies that are easily accessible.

“The reason why cell phones are so cheap is because their technology can be replicated in scale. This is exactly the same for our sensor, which is the only custom part in the whole process,” Iberite said.

And for Francesca Rossi from Bologna, Italy, another participant in the 2023 study who experienced the sensation of touch with temperature in her absent hand, the experience proved to feel transformational.

“Feeling the temperature variation is a different thing, something important, something beautiful. It does not feel phantom anymore because your limb is back,” she said.

To read the study’s complete findings, visit the link here.